704 
Hill and de Fraine. — On the 
Callitris. All the species of this genus examined had two cotyledons 
and a primary diarch root. 
Callitris Muelleri , Benth. & Hook, resembles Thuja orientalis . The 
transition-phenomena are identical, and, as regards the structure of the 
cotyledons, there is the same indication of a few centripetal xylem elements 
in the vascular strands of some individuals ; these elements, both in this 
and in other species, are very poorly marked indeed. Transfusion tissue in 
all the species examined is fairly abundant. 
Callitris calcarata , R. Br., is like the foregoing species, but the phloem 
of each cotyledon-bundle bifurcates towards the base of each seed-leaf. 
The protoxylem assumes the exarch position in the same manner as 
obtains in Juniper us , i.e. the metaxylem passes inwards more rapidly 
than does the protoxylem, and there is a disappearance of some of the 
Diagram 6. Actinostrobus pyramidalis. 
more externally situated metaxylem elements. The assumption of the 
exarch position of the protoxylem, both in this and in the above species, 
takes a relatively long time. 
Callitris robusta , R. Br., closely resembles C. calcarata. The vascular 
strand of a cotyledon of one individual showed not only a bifurcation 
of the phloem, but also a division of the wood, accompanied by a certain 
amount of rotation of the protoxylem to take up the exarch position, while 
the bundle was still contained within the seed-leaf. The trace of the other 
cotyledon behaved in the manner described for C. calcarata. 
In all the species of Callitris examined there are the same variations 
regarding the difference in the phase of each seed-leaf bundle at the same 
level in the same and in different individuals that have already been 
mentioned in the case of Juniperus and Cupressus. 
